1. Field of the Invention
This invention relates to a method for mounting through an adhesive sheet an electronic component on a printed circuit board provided with a wiring pattern.
2. Description of Related Art
In implementation of a general COF (Chip on Film) mounting method, an anisotropic conductive film 14 is bonded onto a flexible board 13 formed with wiring patterns 11 corresponding to electronic component terminals and a solder resist 12 formed in a manner to surround an area to be mounted with electronic component and to cover the wiring patterns 11, as shown in FIG. 1A, while an electronic component 16 having bumps 15 is positioned and placed on the anisotropic conductive film 14, thereby being subjected to thermocompression bonding as shown in FIG. 1B. An electronic component mounting module such as shown in FIG. 1C is therefore obtained.
In the meanwhile, in the COF mounting method as described above, air may remain between the anisotropic conductive film 14 and the flexible board 13 due to uneven surface created by the wiring pattern 11, the solder resist 12, and so on as shown in FIG. 1B. When the electronic component 16 is mounted in such a state, such problems may occur that the air trapped between the anisotropic conductive film 14 and the flexible board 13 expands due to heat and pressure added at a mounting time, thereby forming a void 17, or at worst, the void bursts to destroy the anisotropic conductive film 14, thereby resulting in exposure of the wiring pattern 18. The void 17 or exposure 18 of the wiring pattern leads to decrease in reliability of the electronic component mounting module.
Hence, to prevent such problems as described above, a technology has been proposed in which the trapped air is released to an exterior by forming holes in a thickness direction of the flexible board (see, e.g., Patent Literature 1, Japanese Patent Laying-Open No. H05-343844). According to Patent Literature 1, the ventilation holes are formed in a thickness direction in an area to be connected to a flexible circuit board when bonding and uniting an inflexible circuit board to the flexible circuit board through the anisotropic conductive film. With the connecting method according to Patent Literature 1, therefore, even if a bubble (air) remaining at a contact surface between the inflexible circuit board and the flexible circuit board expands due to application of heat, for example, the air bubble diffuses and outgases easily through the ventilation hole in the area to be connected to the flexible circuit board without remaining in the above described area.
However, the above described method according to Patent Literature 1 requires a superfluous process to previously form or process the holes on the flexible board, thereby having such a problem as complicating the mounting operation. Thus, required is development of an art to solve the problem described above with a means different from the method described in Patent Literature 1.